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Defence researches audio warning in the cockpit

October 26, 2016

Cockpit audio warnings are in English only.

A woman’s voice speaks in monotone; she says “altitude” twice, followed by “bingo” twice, followed by “flight controls” twice. Her tone changes to a more urgent tone, she says “pull up” twice and “roll right” twice.

When it comes to cockpit audio warnings, is the male or female voice more effective for getting the attention of pilots? This is something investigated by scientists at Defence Research and Development Canada (DRDC), Toronto Research Centre.

Auditory warnings are used in aircraft to alert the crew to hazards and their levels of danger. Failing to comply with a warning has led to aviation incidents and accidents.

Given that little is known about the effects of the acoustic parameters of verbal cockpit warnings on perceived urgency, Robert Arrabito, a Defence Scientist in the Human-Technology Interaction Group at DRDC Toronto Research Centre, investigated the effects of talker gender and voice style of verbal cockpit warnings on performance to help make warning messages distinct from speech on the flight deck.

Had there been an aviation incident or accident that prompted the CAF to request you to undertake this type of research? “No, this was part of our research program; the Human-Technology Interaction Group conducts and guides research and development to optimize human technology interactions for the CAF,” said Arrabito.

In the past, it has been said it is easier to pick out the female voice from amid the flurry of radio chatter, but further research has proven otherwise. The increasing role of females in various aviation occupations in the CAF necessitated a re-examination of talker sex and intonation of warning messages to determine their applicability for male and female listeners. This information becomes important when you are talking about warnings that could avoid a catastrophic event.

Arrabito and his team had participants monitor the auditory channel and identify the verbal warning while they were performing a visual task. A male and female actor annunciated each warning word in three voice styles: monotone, urgent, and whisper style. In the first of two experiments, the warning words were presented in a quiet background, and in the second experiment, the warning words were presented in a background of speech babble which simulated cockpit radio communication.

The results of the first experiment showed that the monotone and urgent styles resulted in the fastest identification response time regardless of the talker and listener’s gender. The second experiment showed the male talker annunciating warnings in either the monotone or the urgent style resulted in the largest proportion of correct and fastest identification response time regardless of the listener’s gender.

“If there are no competing background sounds, it doesn’t matter the sex of the talker annunciating the warnings,” said Arrabito. “But when you start to introduce speech babble, the sex of the talker annunciating the warnings of the talker becomes important. Various warnings by male and female showed listeners responded better to the male voice than the female. But that was in one particular study, so we can’t make a general assumption as to what voice type is better.”

The conclusion of this study was that the effective use of speech parameters and word semantics can increase the importance of verbal cockpit warnings.

Non-verbal warnings also studied

Arrabito also studied non-verbal warnings, where he investigated pilots’ judgement of urgency of the warnings in the CH-146 Griffon helicopter.

“We got to fly every day during the study and experience what the pilot and co-pilot would hear on the flight deck and how they respond to certain warnings,” said Arrabito. “Some warnings weren’t loud enough to get your attention, but interestingly enough, those warnings were meant to be very important, where as another warning was quite loud and didn’t have as near as much importance.”

Are speech warnings better than non-speech warnings? “The two types of warnings have their own advantages and disadvantages,” said Arrabito. “With verbal warnings, you have an added advantage that the verbal warning can identify the alarmed condition and state corrective action. But, verbal warnings have their own set of problems because channels of speech communication in the cockpit are often overloaded and as such speech warnings may not be distinct from speech on the flight deck.”

The tested Griffon pilots told the researchers that the warnings which sounded the most urgent to them were indeed the ones that had the least importance assigned to them. The problem of conveying appropriate levels of urgency in non-speech warnings is also experienced in hospital operating rooms; anesthesiologists depend on auditory warnings to alert them to critical changes in the patient’s physiological condition.

“They have the same problem: the sounds that convey the most urgent warning may not necessarily be the loudest,” he said. “Non-verbal warnings are designed independently of each other. Lab studies have been carried out over many years, but in many instances non-verbal warnings are poorly designed because they do not connote the appropriate level of urgency.”

Arrabito continues to conduct research on auditory displays in support of the CAF. “It’s a lot of fun and I get to work with amazing individuals,” he said.

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